When I touch the housing of my amp with my test light it lights up
The ground is self tapped to floor of tahoeThat could be good or bad. Is the test amp hooked up to 12v+? If that's the case, then you're just completing te circuit.
The ground is self tapped to floor of tahoe
You may need to find a more secure ground location.Self tappers are usually not very secure for a ground and usually a poor source on sheet metal. Find a bolt that that is more towards the frame section of the vehicle and utilize that with washers and a terminal ring cleaned from paint ect.The ground is self tapped to floor of tahoe